Movement disorders such as epilepsy and Parkinson's disease have been estimated to affect some 1–2% of the developed world's population and up to 10% of people in underdeveloped countries. Currently, approximately 75% of those who suffer from movement disorders are responsive in some degree to drugs.
Electrical stimulation has also been utilized to treat some movement disorders. In the treatment of epilepsy, studies have been performed in which awake patients undergoing temporal lobe surgery underwent cortical stimulation. Such stimulation of the visual and hearing areas of the brain reproducibly caused the patients to experience visual and auditory phenomena. This discovery was made possible by the identification that certain brain subregions served specific functions, such as sight, hearing, touch and movement of the extremities and proved that direct electrical stimulation of the brain regions could cause partial reproduction or suppression of the functions.
As suggested by these results, it is known that certain types of treatment of specific portions of the brain are able to suppress certain unwanted behavior which results from movement disorders. This behavior may include seizures such as those suffered by epileptics. However, the studies faced a major problem in that there was an inability to precisely electrically stimulate very small volumes of the brain.
The advent of needle-shaped penetrating depth electrodes helped to overcome this obstacle faced by electrical stimulation. Depth electrodes can be placed within the brain tissue itself, enabling optimal surface contact with elements of the brain that are targeted for stimulation. This allowed for safe, chronic electrical stimulation of very small discrete volumes of brain.
In treatment, electrical stimulation has been used with the recording and analysis of changes in brain activity to predict the occurrence of epileptic seizures. The time of onset of such seizures is often predictable by neural discharge monitoring, even when the exact causal nature of precipitating dysfunction is not understood. Electrodes have been used to obtain signals representative of current brain activity along with a signal processor for continuous monitoring and analysis of these electrical signals in order to identify important changes or the appearance of precursors predictive of an impending change.
While the electrical stimulation of brain tissue has been somewhat effective in the treatment of migraines, epilepsy and other neurological problems, patients often experience diminishing returns with such treatment. Furthermore, because each patient reacts differently to electrical stimulation, substantial time must be spent to determine the specific amplitude, frequency, pulse width, stimulation duration, etc. which may result in effective treatment. In addition, such parameters often require continual adjustment in order to remain effective.
Improved intracranial monitoring devices have been shown to facilitate treatments of movement disorders. Monitoring is typically performed by instruments which are inserted into the brain at different locations or along different tracks. Other systems employ a single device which must be removed and reinserted to provide for delivery of multiple drugs or use of different electrical devices.
Since the introduction of probes or other similar devices into the brain is common in many surgical procedures today, there are a variety of probes available. Such probes typically include ports for drug delivery or electrical, chemical, electrochemical, temperature and/or pressure contacts which enable the observation and analysis of the brain state or contacts providing stimulation. These ports and contacts must typically be positioned at specific points or regions in the brain.
Probes used in intracranial penetration are typically fabricated so that their introduction to the brain is as minimally traumatic as possible. In addition to being minimally traumatic during insertion, certain inserted probes must also be able to remain implanted without causing injury through unintended movement. In some uses, a probe may be implanted and remain in the patient's brain for weeks or longer. Changes in the positioning of the probe often occur during placement or during such extended periods. Therefore, the probe must be capable of precise placement and as bio-compatible as possible. In response to these requirements, state of the art intracranial probes are typically thin, flexible pieces with smooth surfaces to minimize the amount of brain tissue contacted and to minimize damage to contacted brain tissue.
While such thin, flexible probes are sufficiently bio-compatible, they are delicate and often difficult to insert along specific trajectories or lines of insertion. During typical implantation, a surgeon feeds the probe into the brain through an aperture in the skull. In this process, the surgeon has very little control over the distal end of the probe. In order to provide more rigidity to the probe to overcome this problem, a removable stylet may be inserted into the probe before implantation. Still, veering from the intended line of insertion is not altogether prevented by introduction of a stylet to the probe.
There is a continuing significant need in the field of intracranial treatment, particularly with insertion of probes into the interior of the brain, for improvements in accuracy of insertion and avoidance of injury, while retaining efficiency and ease of use.
In addition, there is a need in the field of intracranial treatment to minimize the invasiveness of intracranial treatment and to reduce the number of instruments which penetrate brain tissue or the number of times a single instrument must penetrate brain tissue.
Furthermore, there is a need in the field of intracranial treatment to provide the ability to precisely locate the position of a probe during insertion to ensure proper positioning.